In the past, many attempts have been made to design and construct scaffolding that is not only economical to manufacture but also reliable and easy to move, assemble, dis-assemble, and adjust. One problem is that, in order to make scaffolding economical and easy to assemble, dis-assemble, and adjust, the tolerances between many respective parts should be relatively loose. As a result, the assembled scaffold can be structurally weak, shaky, and unreliable. Platforms within the scaffolding and other structure can fall out of the structure during assembly, dis-assembly, and use of the scaffolding to support persons or materials. This type of design trade-off, between (a) economics and ease of assembly, movement, adjustment, and dis-assembly versus (b) structural rigidity, strength, integrity, and safety, has long been a well known and obviously serious concern in the scaffolding art.
For example, much work has been done to try to improve the mechanisms for securing the scaffolding platform to the support legs in a reliable, strong, adjustable, economical, and easily assembled and dis-assembled fashion. Examples of these efforts are shown in U.S. Pat. No, 409,167, 5,028,164, and 4,793,438. All have met with limited success.
For example, the scaffold shown in U.S. Pat. No. 409,167 has support arms at an acute angel to the platform supported by the arms with a bent arm section penetrating apertures in the support legs perpendicularly to the axis of the support legs. The support arms of this structure are thin, relatively flexible, and as a result, non-stable. The bent arm is also subject to significant bending forces that could cause the arm to bend out of position or shear, in which event the scaffold would likely collapse. In addition, the platform of this scaffold is supported only by the relatively thin and angled bent arms in cooperation with four wooden-plank support legs. The structure would not reliably support the relatively large quantities of weight that operators often seek to place on scaffolding today.
The scaffold connection shown in U.S. Pat. No. 5,028,164 has a stronger connecting mechanism for securing the platform to the legs. The legs, however, must have multiple, relatively costly cup-shaped supporting structures in any of the positions in which the platform will be secured along the axial length of the legs. The cup-shaped structures surround the entire leg. They serve as hooks for mating inverted hooks mounted in a complicated, cooperative housing, which includes a spring-loaded latch to lock the inverted hooks and housing in place on the cup-shaped supporting structures. This structure is not only relatively complicated and costly to manufacture, but also difficult, and perhaps impossible, to utilize in a scaffold in which the platform must be readily adjustable along the length of the support legs. This scaffold connection cannot slide along the surface of the legs (due to the cup-shaped hooks) to provide easy adjustment of the height of the platform. This structure also would provide a safety concern if unutilized cup-shaped hooks protrude along the axial length of the legs in areas where persons would be working on a platform supported by the legs.
The scaffold of U.S. Pat. No. 4,793,438 has a connecting mechanism that slides along the support legs and connects to a platform support beam. The support beam is slidable up and down, along with the connecting mechanism, along the support legs. The connecting mechanism has a spring-biased slidable pin that penetrates the support legs perpendicularly to the axis of the support of legs (i.e., parallel to the plane of the platform). As the scaffold is utilized, however, this slidable pin can slide horizontally out of position during assembly, dis-assembly, or use, which can create quite a dangerous situation. This slidable pin and pin housing also does not itself significantly prevent relative horizontal motion between the connecting mechanism and support legs. The pin housing does not itself provide any acute-angled structural connection and support for the central section of the platform and instead utilizes a separate beam for this purpose. In addition, even when assembled, this scaffold allows significant play or movement between the platform and support legs due to, among other things, the lose tolerance between the slidable connecting assembly and the support legs.
Applicant has utilized scaffolds of the type shown in U.S. Pat. No. 4,793,438 and, due to the significant play or movement described above, has observed the platform fall out of this type of scaffold when assembled and in use. This type of play and movement in prior art structures has long provided a significant and dangerous problem to those who use or are in the vicinity of such scaffolding.